GB2544274A

GB2544274A - Method for manufacturing LED devices

Info

Publication number: GB2544274A
Application number: GB1519678.5A
Authority: GB
Inventors: Zahn Michael; Cunnusamy Jessen; Tong Koh Choon
Original assignee: ASM Assembly Systems Switzerland GmbH
Current assignee: ASM Assembly Systems Switzerland GmbH
Priority date: 2015-11-06
Filing date: 2015-11-06
Publication date: 2017-05-17
Also published as: GB201519678D0

Abstract

A method for manufacturing LED devices from multiple LED dies 14 mounted on a substrate comprises the steps of positioning a reflector-printing stencil 32 over the substrate 12 such that a plurality of apertures 34 in the reflector-printing stencil corresponds to gaps between adjacent LED dice positioned on the substrate. Thereafter, a reflector material 38 is printed onto the substrate through the plurality of apertures of the reflector-printing stencil into the gaps between the adjacent LED dice. A layer of phosphor material may be deposited by another printing step wherein the phosphor coating to the LEDs may be applied through a phosphor printing stencil. The stencil may feature a number of setbacks to protect the LED whilst the coating is being applied. The reflector material may be pushed across the reflector printing stencil with a squeegee similar to screen printing. A shim maybe positioned on the substrate prior to the stencil being positioned.

Description

METHOD FOR MANUFACTURING LED DEVICES Field of the Invention

Tile invention relates to the manufacture of li|ht-emitting diode (“LED”) devices, and in particular to LEO devices which comprise reflector layers.

Background and Prior Art

The adoption Of LED devices or modules in lighting applications is becoming more common. The LED devices usually comprise LED chips that are mounted on substrates. The LED chips are typically surrounded by white reflector layers which may comprise a mixture of titanium pile and other compounds to distribute the light that is emitted by the LED chips and to enhance the illumination effect. As the LED chips do not naturally emit white Sight, a phosphor coating is formed over the LED chip to adjust the colour emitted by the LED chip and to render white iight.

In the prior art, such as that described in US Patent Number 8,921,13162 entitled “Method for Manufacturing Light Emitting Diode Package”, there is described a method for manufacturing an LED package method which comprises the steps of providing a substrate, forming a reflector on the substrate with a receiving chamber defined in the reflector, and then mounting an LED chip in the receiving chamber and covering the receiving chamber including the LED chip with a gelatinous phosphor layer. A pressing mold is used to compress the phosphor layer to fill the receiving chamber before solidifying it. Finally, the LED chips are separated from one another by singulation.

The formation of the reflector on the substrate in the method described above is conducted by way of injection molding or transfer molding. However, the use

Of injection molding or transfer molding has certain shortcomings, as explained below.

In ort| type of LEO decile, the LED chip is completely surrounded by the reflector layer. Thus, it is necessary to form the reflector layer only after the LED chip has been mounted onto the substrate, rather than mounting the LED chip into a recess in the reflector layer. Moreover, such type of LED device requires the thickness of the reflector layer to be at substantially the same height p the top surface of th| mounted LED chip.

With such requirements, the molding process may become difficult and slow. Since the molding process is not sufficiently precise, one approach for molding the reflector layer is to mold the reflector layer to a thickness that is higher than a tip surface of the LED Chip. Thereafter, fie excess reflector material is grinded down until the top of the LED chip is exposed Not only is this method cumbersome and slow the grinding process risks damaging the LED chip.

Besides melding* another approach is to dispense the reflector materia! between lip LED chips using a nozzle, but height control of the dispensed reflector layer is still a problem. Besides being slow and resulting in low throughput, both these approaches require expensive special-purpose machines such as molding and grinding: machines to implement, and they are thus not cost-effective.

Next, a layer of phosphor should be formed over the top surfaces of the LED chips before they are separated from one another conventional approaches such as the aforesaid compression molding or an alternative of spraying a phosphor coating onto the LED chips are undesirable. First, phosphor materia! is expensive and molding results in wastage of the material. Likewise, spraying is imprecise and wastes phosphor material because the whole substrate needs to be sprayed. Furthermore, edge sharpness is not well-controlled, resulting in quality problems at the edgls of the LED chips Moreover, both processes are quite slow.

It would be beneficial to seek a method for manufacturing LED devices which is faster and more cost-effective than the foregoing

Summary of the Invention

It is thus an object of the invention to seek to devise a method of manufacturing LED devices that overcomes at least some of the disadvantages of the prior art.

According to a first aspect of the invention, there is provided a method for manufacturing LED devices from multiple LED dice mounted on a substrate, the method comprising the steps oft positioning a reflector-printing stencil over the substrate such that a plurality of apertures in the reflector-printing stencil corresponds to gaps between adjacent LED dice positioned on the substrate; and thereafter printing a reflector material onto the substrate through the plurality of apertures of the reflector-printing stencil into the gaps between the adjacent LED dice.

According to a second aspect of the invention, there is provided a method for manufacturing LED devices from multiple LED dice mounted on a substrate, the method comprising the steps of: positioning a first stencil over the substrate such that a plurality of apertures in the first stencil corresponds to gaps between adjacent LED dice positioned on the substrate; printing a first materia! onto the substrate through the plurality of apertures of the first stencil into the gaps between the adjacent LED dice; removing the first stencil and positioning a second stencil over the substrate such that a plurality of apertures in the second stencil corresponds only to locations of top surfaces of the LED dice; printing a second material onto the top surfaces of the LED dice to form a coating comprising the second material on the top surfaces of the LED dice;

In! thereafter removing the second stencil and singulating the LED dice from one another to form separate LED devices.

It would be convenient hereinafter to describe the invention in greater detail by reference to the accompanying drawings which illustrate specific preferred embodiments of the invention. The particularity Of the drawings and the related description is not to be understood as superseding the generality of the broad identification of the invention as defined by the claims.

Brief Description of the Drawings

An example of a method for manufacturing LED devices in accordance with the invention will now be described with reference to the accompanying drawings, in which: FIG. 1 is an isometric view of an exemplary LED device including a phosphor film coated on an LED dief FIG, 2 is a plan view of a reflector-printing stencil for printing a reflector materia! between multiple LED dice according to a first preferred embodiment of the invention; FIG. 3 is a cross-sectional view of the reflector-printing stencil positioned over a substrate including multiple LED dice for printing reflector material onto the substrate; FIG. 4 is a plan view of the substrate including multiple LED dice which has a iapr of printed reflector material filling the gaps between the LED dice according to the first preferred embodiment of the invention; FIG 5 is a cross-sectional View of the substrate of FIG. 4; FIC3. 8 is a plan view of a refiector-printing sienci! for printing reflector material according to a second preferred embodiment of the invention; FIG, 7 j§ a pian view of a shim including dividing barriers that is usable together with the reflector-printing stencil illustrated in FIG. 8; FIG. 8 is cross-sectional view of the shim and the refiector-printing stencil positioned over a substrate including multiple LED dice for printing reflector material onto the substrate; FIG; 9 is a plan view of the substrate including multiple LED dice which has a layer df printed reflector material filling the gaps between the LED dice according to the second preferred embodiment of the invention; FIG. 10 is a cross-sectional view ofthe substrate of FIG. 9; FIG. 11 is a plan view of a phosphor-printing stencil for printing phosphor material onto multiple LED dice according to fee preferred embodiment of the invention; FIG. 12 is a cross-sectional view of the phosphor-printing stencil positioned over the substrate for printing phosphor material onto the LED dice; FIG, 13 is a plan view of a substrate which has a layer of printed phosphor material coated onto each LED die mounted on the substrate; and FIG. 14 is a cross-sectional view of the substrate of FIG. 13,

Detailed Description of the Preferred Embodiment of the Invention FIG. 1 is an isometric view of ari exemplary LED device 10 including a phosphor film 30 coated on an LED die 14. The LED die 14 is generally supported on a carrier substrate 12 and is electrically connected to electrical contacts on tie carrier substrate 12 via solder humps 16.

The LEE) die 14 includes respective p-electrodes 18 and n-electrodes 2| that are in contact with the solder humps 16. Further, the p-electrodes 18 are connected to a p-Gallium Nitride layer 22 and the n-electrodes 2i are connected to an n-Gallium Nitride layer 24. There are other active layers 26 comprised in the LED die 14 ^depending on its composition) with a sapphire substrate 28 generally located at the top of the LED die 14. The sapphire substrate 28 is finally coated with a phosphor layer 30 on its top surface for adjusting the colour of the light emitted by the LED die 14. FIG. 2 is a plan view of a first stencil in the form of a refiector-printing stencil 32 for printing a first material, such as a reflector material, between multiple LED dice 14 according to a first preferred embodiment of the invention. The r|f|i|tonprinting stencil 32 comprises a plurality of apertures 34 corresponding to gaps between adjacent LED dice 14 for releasing reflector material through the reflector-printing stencil 32 onto a carrier substrate or substrate 12 underneath it. A plurality of setback regions 36 without apertures are formed at locations which correspond to positions of LED dice 14 on the substrate 12 when the reflector-printing stencil 32 is placed over the substrate 12 so that the setback regions 36 cover top surfaces of the LED dice 14 when printing the reflector material. This avoids reflector material from being released onto the LED dice 14. The reflector-printing stencil 32 used may be the one described in US Patent Publication number 2015/165756 entitled “Stencils”. FIG. 3 is a cross-sectionai view of the reflector-printing stencil 32 positioned over a substrate 12 including multiple LED dice 14 for printing reflector material 38 onto the substrate 12. The setback regions 36 of the reflector-printing stencil 32 are positioned to cover the top surfaces of the LED dice 14, whereas f!H apertures 34 are positioned over gaps between adjacent LED dice 14. Reflector material 38 is provided on the reflector-printing stencil 32 and a squeegee 40 pushes the reflector material 38 across the top surface of the reflector-printing stencil 32.

As the squeegee 40 pushes |h| reflector material 38 over the apertures 34 fp print reflector materia! 38 onto the substrate 12, the reflector material 38 fil! the plurality of apertures 34 and land on the substrate 12 underneath, thereby filling the gaps between the adjacent LED dice 14 The squeegee 40 pushes the reflector material 38 across the whole surface of the reflector-printing stencil 32 in order to fill all the apertures 34 After printing, the reflector printing stencil 32 is removed from the substrate 12 and LED dice 14. FIG. 4 is a plan view of the substrate 12 including multiple LED dice 14 which has a layer of printed reflector materia! 42 filling; the gaps between tie LED dice 14 according to the first preferred embodiment of thi invention. FIG. 5 is a cross-sectional view of the substrate 12 of FIG. 4. It illustrates that a top surface of the layer of printed reflector material 42 is substantialiy flush with the top surfaces of the LED dice 14 FIG. 6 is a plan view of a reflector-printing stencil 44 for printing reflector material 38 according to a second preferred embodiment of the invention. In this second embodiment, instead of entirely filling the gaps between adjacent LED dice 14 with reflector material, trenches are created to better-define separate LED devices 10 and also to reduce the use of reflector material. Thus, whilst the reflector-printing stencil 44 comprises apertures 48 and setback regions 18 as in the first embodiment, it also comprises dividers 49 which define outlines separating the respective LED devices 10. Reflector material 28 will not be printed along the positions of these dividers 49. FIG. 7 is a plan view of a shim 50 including dividing barriers 52 that is usable together with the refiector-printing stencil 44 illustrated in FiG. 6. the lines of the dividing barriers §2 coincide with the lines of the dividers 41 when the reflector-printing Stencil 44 is positioned onto the shim Si, and they are stacked on the substrate 12. Preferably, a height of the shim 50 corresponds substantially to heights of the top surfaces of the LIE) dice 14 located on the sulstrate 12.

Flit, 1 is cross-sectional view of the shim 5| and the reflector-printing stencil 44 positioned over a substrate 12 including multipie LED dice 14 for printing reflector material IS onto the substrate 12. The shim SO is placed directly onto the substrate 12, whereas the reflecton-pinting stencil 44 is placed onto the Shim 50.

As illustrated in FI©, 8, the dividing barriers 52 are positioned approximately equidistant between adjacent LED dice 14 and prevent reflector material 31 from being printed onto positions covered by the dividing barriers 52. On top of the shim 50, the setback regions 41 of the reflector-printing stencil 44 are positioned to cover the top surfaces Of the LED dice 14, and the dividers 49 are positioned to cover the top surfaces of the dividing barriers 52. The apertures 46 are positioned over gaps between adjacent LED dice 14.

Reflector material 38 is provided on the reflector-printing stencil 44 and p squeegee 40 pushes the reflector material 38 across the top surface of the reflector-printing stencii 44. As the squeegee 40 pushes the reflector material 38 over the apertures 46, the reflector material 38 fill the apertures 46 and land on the substrate 12 underneath, thereby filling the gaps between the adjacent LED dice 14, except for the areas covered by the dividing barriers 52. The squeegee 40 pushes the reflector materia! 38 across the whoie surface of the reflector-printing stencil 32 in order to fill ||l the apertures 34. After printing, the reflector-printing stencil 44 and shim 50 are removed from the substrate 12 and LED dice 14. FIG. 9 is a plan view of the substrate 12 including multiple LED dice 14 which has a layer of printed reflector material 42 filling the gaps between the LED dice 14 according to the second preferred embodiment of the invention, In this embodiment, there are trenches P- between blocks of printed reflector material 42 corresponding to the locations of the dividing barriers 52 during printing. FIG. 10 is a cross-sectional view of the substrate 12 of FIG. 9. It illustrates that a top surface of the layer of printed reflector material 42 is substantially flush with the top surfaces of the LED die© 14. The trenches 54 between blocks of printed reflector material 42 are also illustrated more clearly.

FiG. 11 is a plan view of a second stencil in the form of a phosphor-printing stencil 56 for printing a second material, such as phosphor material, onto multiple LED dice 14 according to the preferred embodiment of the invention. The phosphor-printing stencil 56 comprises a plurality of groups of apertures 58 which are formed only at locations corresponding to locations of the LED dice 14 on the substrate 12. The printing of phosphor material may occur after the printing of reflector material according to the first or second preferred embodiments of the invention described above; and is applicable to either embodiment. FIG 12 is a cross-sectional view of the phosphor-prihting stencil 56 positioned over the substrate 12 for printing phosphor material 60 onto the LED dice 14. The groups of apertures 58 Of the phosphor-printing stencil 56 are positioned to cover the top surfaces of the LED dice 14. Thus, only the top surfaces of tie LED dice 14 will be coated with phosphor material 60, whereas the areas where the printed reflector material 42 are situated will not be coated. Phosphor material 60 is provided on the ih|sphor-prihting stencil 56 arid a squeegee 40 pushes the phosphor material 60 across the top surface of the phosphor-p ri nti ng stencil 56.

As the squeegee 40 pushes the phosphor material 38 over the groups of apertures 58, the phosphor material 38 fill the apertures Si and land on the top surfaces of the LED dice 14 underneath, thereby coating the top surfaces of the LED dice 14 with a film of phosphor. The squeegee 40 pushes the phosphor material 60 across the whole surface of the phosphor-printing stencil 56 in ordff fo fill all the group of apertures 58. After printing, the phosphor-pnnting stencil 56 is removed from the substrate 12 and LED dice 14. FIG, 13 is a plan view of a substrate 12 which has a layer of printed phosphor material 62 coated onto each LED die 14 mounted on the substrate 12. Eli, 14 i 1 cross-sectional view of the substrate 12 of FIG. 13, which further illustrates the layers of printed phosphor material 62 coated over and above the flushed top surfaces of the LED dice 14 and printed reflector material 42. Thereafter, the substrate 12 may be singuiated to firm separate LED devices 10 from the multiple LED dice 14.

The LED industry is continuously searching tor opportunities to save costs and to produce components faster to satisfy market needs. Hence, manufacturers must always seek to increase production throughput and to lower the cost price.

By applying the method as disclosed in the preferred embodiments of the invention to coat the layer of printed reflector material 42 for an LED device 10 and to coat the lapr of printed phosphor material 62 thereafter, many of the obstacles faced by the conventional approaches to manufacturing an LED device 10 are avoided. The said method is also assisted by the fact that the printing process is straightforward, it makes use of relatively inexpensive stencils 32, 44, 56 to dispense the materials more precisely, and a standard printing platform (which is also relatively inexpensive) may be utilized to increase reliability and efficiency while reducing operating costs. in general, printing is a quick and very cost effective method to deposit the reflector and phosphor materials as compared to prior art methods of depositing the same. The method is particularly advantageous for depositing reflector material 38 to surround the LED dice 14. By providing an LED device manufacturing process that can be completed by printing, it further aids adoption of the technology as part of an in-line solution for significantly increasing throughput and production quantities at lower oost as compared to the prior art.

The invention described herein is susceptible to variations, modifications and/or additions other than those specifically described and it is to be understood that tie invention includes ail such variations, modifications and/or additions which fall within the spirit and scope of the above description.

Claims

CLAIMS:

1. Method for manufacturing LED devices from multiple LED dice mounted op § substrate, the method comprising the steps of: positioning a reflector-printing stencil over the substrate such that a plurality Of apertures in the reflector-printing stencil corresponds to gaps between adjacent LED dice positioned on the substrate; and thereafter printing a reflector materia! onto the substrate through the plurality of apertures of the reflector-printing stencil into the gaps between the adjacent LED dice.
2. Method for manufacturing LED devices as claimed in claim 1, wherein the stencil includes a plurality of setback regions that cover the LED dice when printing the reflector material to avoid printing the reflector material onto the LED dice.
3. Method for manufacturing LED devices as claimed in claim 1, wherein the step of printing the reflector materia! further comprises the step of providing the reflector material on the reflector-printing stencil and pushing the reflector material across a top surface of the reflector-printing stencil with a squeegee so that the reflector material falls through the plurality of apertures onto the substrate underneath the reflector-printing stenci!.
4. Method for manufacturing LED devices as claimed in claim % wherein the reflector material is printed such that a top surface of the reflector material that is printed is substantially flush with top surfaces of the LED dice.
5. Method fdr manufacturing LED devices as claimed in claim 1, further comprising the step of placing a Shim onto the substrate prior to positioning the reflector-printing stencil over the suhstpte, wherein the shim comprises dividing barriers which prevent the reflector material from being printed onto positions covered by the dividing barriers of the shim.
6. Method for manufacturing LED devices as claimed in claim 5, wherein the dividing harriers are positioned substantially equidistant between adjacent LED dice. % Method for manufacturing LID devices as claimed in claim 5, wherein a height of the shim corresponds substantially to heights of top surfaces of the LED dice.
8. Method for manufacturing LED deices as claimed in claim 5, wherein the reflector-printing stencil further comprises dividers which correspond to positions of the dividing barriers of the shim when the reflector-printing stencil is positioned onto the slim. i. Method for manufacturing LED deices as claimed in claim 1, wherein after printing the reflector material onto the substrate! the method further comprises the steps of: removing the reflector-printing stencil and positioning a phosphorprinting stencil over the substrate such that a plurality of apertures in tie phosphor-printing stencil corresponds only to locations of top surfaces of tie LED dice- printing a phosphor material onto the top surfaces of the LED dice to form a coating comprising the phosphor material on the top surfaces of the LED dice; and thereafter removing the phosphor-printing stencil and singulalng the LED dice from one another t| form separate LED devices.
10. Method for manufacturing LED devices as claimed in claim §, wherein the step of printing the phosphor material further comprises the step of providing the phosphor material on the phosphor stencil and pushing the phosphor material across a top surface of the phosphor-printing stencil with a squeegee so that the phosphor material falls through the plurality of apertures onto the LED dice underneath the phosphor-printing stencil.
11. Methei for manufacturing LED defiefs from multiple LED dice mounted on a substrate, the method comprising the steps of: positioning a first stencil over the substrate such that a plurality of apertures in the first stencil corresponds to gaps between adjacent LED dice positioned on tee substrate; printing a first material onto tee substrate through the plurality of apertures of the first stencil into the gaps between the adjacent LED dice; removing the first stencil and positioning a second stencil over the substrate such that a plurality of apertures in the second stencil corresponds only to locations of top surfaces of tee LED dice; printing a second materia! onto the top surfaces of the LED dice to form a coating comprising tee second material on the top surfaces of the LED dice; and thereafter removing the second stencil and singulating the LED dice from one another to term separate LED devices.
12. Method ter manufacturing LED devices as claimed in claim 11, wherein the first stencil includes a plurality of setback regions that cover the LED dice when printing the first material te avoid printing the first material onto the LED dice.
13. Method for manufacturing LED devices as claimed in claim 11, wherein the first material is printed such that a tip surface of the first material that is printed is substantially flush with top surfaces of the LED dice.
14. Method for manufacturing LED devices as claimed in claim 11, further comprising the step of placing a shim onto the substrate prior to positioning the first stencil over the substrate, wherein the shim comprises dividing barriers which prevent the first material from being printed onto positions covered by the dividing barriers of the shim.
15. Method for manufacturing LED devices as claimed in claim 14, wherein the dividing barriers are positioned substantially equidistant between adjacent LED dice.
16. Method for manufacturing LED devices as claimed in claim 14, wherein a height of the shim corresponds substantially to heights of top surfaces of the LED dice.
17. Method for manufacturing LED devices as claimed in claim 11, wherein the first material comprises reflector material and the second material comprises phosphor material.